Engine lubricants containing phosphorus compounds and sulphur have been shown to contribute in part to particulate emissions and emissions of other pollutants. In addition, sulphur and phosphorus tend to poison the catalysts used in catalytic converters, resulting in a reduction in performance of said catalysts.
With increasing control of emissions (emissions often being associated with contributing to NOx formation, SOx formation, formation of particulate matter, formation of ash and reducing the efficiency of after-treatment catalytic converters) there is a desire towards reduced amounts of sulphur, phosphorus and sulphated ash in engine oils. Emission standards such as Euro 4 or Euro 5 further limit the amounts of, for example, sulphated ash, phosphorus, sulphur and particulate matter.
In passenger car vehicles (which may also be referred to as vehicles containing “light-duty internal combustion engines (typically with an engine capacity of 6 liters or less)) the introduction of emission standards such as Euro 4 or Euro 5 is believed to increase the usage of after-treatment devices. After-treatment devices include but are not limited to particulate filters. In addition, the particulate filters are being added to diesel passenger car vehicles.
To reduce poisoning of after-treatment devices with sulphur, phosphorus or excessive amounts of ash, lubricants are required to be formulated with lower levels of sulphated ash, phosphorus and sulphur. The most recent limits on sulphur, phosphorus and ash are described within the 2004 ACEA sequences for light duty engine oils. In particular for the C category (i.e., Catalyst compatible) the limits are amongst the lowest required for a lubricant. Accordingly, the ACEA C1 and C4 are amongst the most demanding specifications to meet.
U.S. Patent Application 2007/0149419 discloses a lubricating oil composition for internal combustion engines, particularly heavy duty diesel (HDD) engines, having reduced phosphorus, sulphur and sulphated ash content that provides excellent piston cleanliness performance and contains an amount of phenate detergent that introduces a relatively large amount of phenate soap into the lubricating oil composition. In addition, the lubricating composition contains sulphonate detergent. Typically at least one of the phenate detergent or sulphonate detergent is a magnesium-containing detergent.
European Patent application 765 931 A discloses a lubricating composition for a heavy duty diesel engine containing a major amount of an oil of lubricating viscosity, a minor amount of a carbonated sulphurised metal alkyl phenate and a minor amount of a carbonated metal alkyl aryl sulphonate, wherein the total base equivalents donated by the phenate is more than 85% of the total equivalents donated by the phenate and sulphonate.
As passenger car engine technology develops, components of an engine are exposed to more severe operating conditions. Operating conditions may include higher power density engines, use of turbo chargers, and use of alternative fuels. Under many severe operating conditions, oxidation of lubricant and components occurs more readily.